In the fourth month of pregnancy, ultrasound examination indicates that the lower edge of the placenta reaches the endocervix. This condition is called placenta previa state, meaning that the placenta is attached in a low position, attached to the lower segment of the uterus. With the prolongation of pregnancy, the placenta may move up with the uterus and become a normal position. Therefore, the lower edge of the placenta reaches the cervical os at four months, and the main thing to observe is vaginal bleeding. If there is no significant vaginal bleeding and little vaginal bleeding, you can continue to wait. Perhaps in the later stages, the placenta will move up to become a normal position placenta due to the stretching of the lower segment of the uterus.